My personal mentor, Alan Emrich, taught me 2 rules of game design, apparently as mentioned by Jim F. Dunnigan, a famous war-game analyst and war game designer. These are:
1) Use Available Resources (steal)
2) K.I.S.S. (Keep it simple, stupid)
It resonates through everything I do as a game designer. Is the game idea "stealing" with good judgement? Is it a "me too" kind of game? Are there too many other games like it? Is it too complicated? Can it be streamlined? Can the game do without this feature?